Short metal arc tube mounted within a ceramic reflector envelope



Feb. 24, 1970 J. F. RICHTER 3,497,742

SHORT METAL ARC TUBE MOUNTED N A CERAMIC FLECTOR ENVEL led Dec. 18 1 WITHI OPE 967 INVENTOR. JOHN F. RICHTER q -2%; Mm ATTORNEYS United States Patent 3,497,742 SHORT METAL ARC TUBE MOUNTED WITI-EEN A CERAMIC REFLECTOR ENVELOPE John F. Richter, San Francisco, Calif., assignor to Varian Associates, Palo Alto, Calif., a corporation of California Filed Dec. 18, 1967, Ser. No. 691,399

Int. Cl. H01 1/02, 7/24 US. Cl. 313-15 ABSTRACT OF THE DISCLOSURE A metal vapor arc lamp comprising a sealed arc tube confining an ionizable alkali metal, two spaced electrodes which penetrate the arc tube to define an arc gap there within, and means for heating the alkali metal to enable a voltage impressed across the arc gap to ionize the heated metal vapor and ignite the arc lamp. The are tube is housed in a sealed envelope having a ceramic cylindrical section hermetically closed at each end by envelope membars which respectively comprise a reflector and an optical window.

BACKGROUND OF THE INVENTION This invention relates to metal vapor arc lamps and particularly to high intensity, short are metal vapor lamps having an integral reflector sealed within a ceramic envelope.

In copending application, Ser. No. 655,717, filed July 14, 1967, a high intensity short arc lamp is disclosed by applicant having a novel envelope comprising a ceramic cylinder hermetically closed at its ends by a reflector and an optical window. Housed within the envelope is an ionizable gas under pressure and two electrodes. This structure provides a high intensity arc lamp having a composite, rugged, integral bulb and reflector devoid of glass-to-metal seals and consisting of material which will not react with the internal atmosphere. The gaseous atmosphere may be an inert gas such as xenon, argon or krypton or a mixture consisting essentially of a metal vapor such as mercury, cesium, rubidium, sodium, potassium or lithium.

The present invention is an improvement in the just described lamp where the ionizable gas is a corrosive metal vapor such as cesium, rubidium, sodium and potassium. These elements are quite eflicient as a source of radiation in the near infrared region of the spectrum. They must, however, be heated above room temperature before an electrical potential will ionize them and ignite the arc. But as the described lamp contains no heating means, an inert gas must be combined with the metal vapor as an ignition catalyst. This addition, however, alters the spectral emission of the lamp thereby diminishing, and in some applications, destroying its utility. Furthermore, high, total, energy conversion efiiciency requires the high metal vapor pressures which are produced by heating of the vapor to temperatures as high as i000 C. As the described lamp has an integral source and reflector, the entire structure has to be heated to achieve the pressure necessary for high conversion efliciency when filled with a corrosive metal vapor.

Accordingly, it is an object of the present invention to provide a high intensity arc lamp having an ionizable gaseous medium of metal vapors uncombined with extraneous catalytic vapors to provide high emission efficiency in the near infrared region of the electromagnetic spectrum.

Another object of the invention is to provide a short arc, high intensity metal vapor lamp capable of operat- 14 Claims- 3,497,742 Patented Feb. 24, 1970 ing at temperatures as high as 1000 C. for high energy conversion etiiciency.

Yet another object of the invention is to provide an improved metal vapor arc lamp having an envelope comprising a ceramic cylinder hermetically closed at its ends by a reflector and an optical window.

SUMMARY 'OF THE INVENTION Briefly described, the present invention is a metal vapor arc lamp comprising a sealed arc tube confining an ionizable metal selected from the alkali metal group consisting of cesium, sodium, potassium and rubidium. Two spaced electrodes penetrate the arc tube to define an arc gap therewithin. Means are provided for heating the ionizable alkali metal to enable a voltage impressed across the arc gap to ionize the heated metal vapor and ignite the arc lamp. The are tube is housed in a sealed envelope having a ceramic cylindrical section hermetically closed at each end by envelope members which respectively comprise an optical window and a reflector.

BRIEF DESCRIPTION OF THE DRAWING FIGURE 1 is a side view in cross section of the preferred embodiment of the present invention.

FIGURE 2 is a frontal view in elevation of the embodiment shown in FIGURE 1.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now in more detail to the drawing, in which figures like reference numerals represent like components, there is shown a metal vapor arc lamp having a ceramic, cylindrical section 10 which is preferably made of polycrystalline alumina and which is brazed to a metallic ring 12 having a flange 14. Ring 12 and flange 14, which preferably are made of Kovar, serve as a section of the lamp envelope and as an exteriorly accessible lamp electrode, respectively. Ring 12 is brazed to a metallic spacer 1-6 which in turn is brazed to window frame 18 also made of Kovar. An optical window 20, in this case glass, is sealed within the window frame. A concentric ring 22 is then joined to frame 16 by heliarc welding to an intermediary ring 23.

The other end of ceramic section 10 is brazed to another Kovar ring 24 through which a copper tubulation 26 extends. A concentric ring 28 is fitted about ring 24 and brazed to ceramic section 10. Finally, the free end of ring 28 is welded by heliarc to the free end of a ring 29 which in turn is brazed to Kovar ring 24.

A paraboloidic reflector 30 having an axial aperture is brazed to an inner edge of ring 24. The reflector comprises a metal base having a very thin coating of gold, silver or platinum. The geometry of the reflector produces a beam divergence limited to but 1 to 2.

One end of a Kovar tube 32 is brazed to the reflector adjacent the aperture periphery. The other end of tube 32 is welded to a cap 34, which in turn is brazed to a ceramic disc 36 having an aperture coaxial with that of reflector 30. An electrode 38, extending through the aperture of disc 36, is aflixed thereto by means of sealing ring 40 to complete the lamp envelope.

A resistive heater wire 42 is wound about a portion of electrode 38. One end of the heater wire is aflixed to the electrode while the other end is aflixed to tube 32. In this manner both electrode 38 and tube 32 serve as exteriorly accessible lamp electrodes, as does flange 14.

Electrode 38 extends within the lamp envelope into an arc tube comprising a transparent, sapphire tube 44 sealed at each end by caps 46 which preferably are made of columbium. Electrode 38 terminates within the arc tube adjacent the terminus of another electrode 48 which extends through the other end cap 46 along the axis of electrode 38. The spacing between the electrodes defines an arc gap which approximates the diameter of the electrodes. This geometry places the lamp in the category commonly referred to as short are.

The arc tube is filled with cesium, sodium, potassium or rubidium. These alkali metals are in a solid state at room temperature. Upon being heated the metals change into their vapor state and typically assume a pressure of some ten standard atmospheres.

The end of electrode 48 outside of the arc tube, but Within the lamp envelope, is brazed to one end of three arcuate supports 50 which are preferably made of Kovar or molybdenum. The other end of supports 50 are brazed to ring 12 providing electrical connection between electrode 48 and flange 14. The arcuate shape of supports 50 permits stress release during high temperature lamp operation.

After assembly, the envelope is evacuated through means of tubulation 26 which is then sealed. Alternatively, the envelope may be backfilled with an inert gas.

The described metal vapor lamp is uniquely suited for use as an intense source of infrared radiation in the spectral region of from 7,500 to 12,000 angstroms. Here full advantage can be taken of the capability of the metal vapor arc tube to operate at high temperatures to produce high vapor pressures which in turn yield increased infrared radiation at a sacrifice in total luminous emission. Thus as a convert source, less visible radiation is produced and more energy is converted to infrared radiation.

It should be understood that the above-described embodiment is merely illustrative of applications of the principles of the invention. Obviously, many modifications may be made in the illustrated example without departing from the spirit and scope of the invention as set forth in the following claims.

What is claimed is:

1. A metal vapor arc lamp comprising an envelope having a ceramic cylindrical section hermetically closed at each end by envelope members, a sealed arc tube housed Within said envelope and confining an ionizable metal selected from the alkali metal group consisting of cesium, sodium, potassium and rubidium, two spaced electrodes penetrating said are tube to define an arc gap therewithin, and means for heating said ionizable alkali metal to enable a voltage impressed across the arc gap to ionize the heated metal vapor and thereby ignite the arc lamp.

2. The metal vapor arc lamp of claim 1 wherein said heating means comprises a resistor Wound in spaced relation about a portion of at least one of said electrodes.

3. The metal vapor arc lamp of claim 2 wherein said resistor is electrically and mechanically connected to the electrode.

4. The metal vapor arc lamp of claim 1 wherein said sealed arc tube comprises a sapphire tube and apertured columbium caps sealed to each end thereof.

5. The metal vapor arc lamp of claim 1 wherein one of said envelope members comprises an optical Window pervious to the passage of infrared radiation.

6. The metal vapor arc lamp of claim 1 wherein one of said electrodes penetrates said envelope.

7. A metal vapor arc lamp having a sealed envelope comprising a ceramic cylindrical section hermetically closed at each end by envelope members, one of said members comprising a first metallic component and an optical Window and the other of said envelope members comprising a second metallic component and an apertured dielectric body, said envelope housing an arc tube which confines an ionizable metal selected from the alkali metal group consisting of cesium, sodium, potassium and rubidium; said are lamp further comprising a first electrode extending through said aperture dielectric body and into said are tube, a second electrode electrically and mechanically connected within said envelope to said first metallic component and extending into said arc tube adjacent said first electrode to define an arc gap therebetween, and means within said envelope electrically coupled to said second metallic component for heating said metal to ignite the arc lamp.

8. The metal vapor arc lamp of claim 7 wherein said heating means comprises a resistor wound in spaced relation about a portion of said first electrode.

9. The metal vapor arc lamp of claim 8 wherein said resistor is electrically and mechanically connected to said first electrode.

10. The metal vapor arc lamp of claim 7 wherein said second metallic component is a tube disposed coaxially about said first electrode to form a by-terminal male connector.

11. A metal vapor arc lamp of claim 7 wherein said are tube comprises a sapphire tube.

12. The metal vapor are lamp of claim 11 wherein said arc tube further comprises apertured columbium caps sealed to each end of said sapphire tube.

13. The metal vapor arc lamp of claim 7 wherein said sealed envelope comprises a reflector defining an aperture and wherein said arc tube extends through said reflector aperture.

14. The metal vapor arc lamp of claim 7 having an arcuate reflector aflixed to said metallic component.

References Cited UNITED STATES PATENTS 2,333,052 lO/1943 Smith 313-15 2,820,164 1/1958 Retzer 313-15 2,982,877 5/1961 Heine-Geldner 313-184 3,138,731 6/1964 Beese 313-113 3,283,202 11/1966 Pennington 315-46 3,364,374 1/1968 Wilson 313-184 3,384,798 5/1968 Schmidt 313-184 JAMES W. LAWRENCE, Primary Examiner C. R. CAMPBELL, Assistant Examiner US. Cl. X.R. 313-25,113,184, 220, 331; 315-46 

